Method for evaluating failure-in-time

ABSTRACT

A FIT evaluation method for an IC is provided. The FIT evaluation method includes accessing data representing a layout of the IC comprising a number of metal lines and a number of VIAs; picking a number of nodes along the metal lines; dividing each of the metal lines into a number of metal segments based on the nodes; and determining a FIT value for each of the metal segments or VIAs to verify the layout and fabricate the IC.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 15/355,410,filed on Nov. 18, 2016 now U.S. Pat. No. 10,157,258.

BACKGROUND

Electro-migration (EM) is one of the most important issues in designingintegrated circuits (ICs). Specifically, EM is the transportation ofmaterial caused by the gradual movement of ions in a conductor due tothe momentum transfer between conducting electrons and diffusing metalatoms. The effect appears in applications where high-current pulses aregenerated, such as in microelectronics and related structures.

The EM effect becomes more apparent as the structure size decreases inelectronics such as integrated circuits (ICs). The EM effect is usuallyevaluated by lifetime and failure rates, and the failure-in-time (FIT)is often utilized to indicate the failure rate of the IC. Therefore, amethod for calculating FIT will be needed to evaluate the EM effect onthe IC.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic diagram of a chip, in accordance with someembodiments.

FIGS. 2A-2B are schematic diagrams of resistors of a metal line, inaccordance with some embodiments.

FIGS. 3A-3B are schematic diagrams for illustrating nodes and metalsegments of a metal line, in accordance with some embodiments.

FIGS. 4A-4B are schematic diagrams for illustrating nodes and metalsegments of metal lines, in accordance with some embodiments.

FIGS. 5A-5B are schematic diagrams for illustrating nodes and metalsegments of a metal line, in accordance with some embodiments.

FIGS. 6A-6B are schematic diagrams for illustrating nodes and metalsegments of a metal line, in accordance with some embodiments.

FIG. 7 is a schematic diagram illustrating current direction with nodesand metal segments of a metal line, in accordance with some embodiments.

FIG. 8 is a schematic diagram illustrating current direction withbranches of metal lines, in accordance with some embodiments.

FIGS. 9A-9B are schematic diagrams for illustrating VIAs and metallines, in accordance with some embodiments.

FIG. 10 is a flow chart of a method illustrating the operations forevaluating FIT value, in accordance with some embodiments.

FIG. 11 is a flow chart of a method illustrating the operations forevaluating FIT value, in accordance with some embodiments.

FIG. 12 is a flow chart of a method illustrating the operations forevaluating FIT value, in accordance with some embodiments.

FIG. 13 is a block diagram of a computer system for evaluating FITvalue, in accordance with some embodiments.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in some various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween some various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Some embodiments of the disclosure are described. Additional operationscan be provided before, during, and/or after the stages described inthese embodiments. Some of the stages that are described can be replacedor eliminated for different embodiments. Additional features can beadded to the semiconductor device. Some of the features described belowcan be replaced or eliminated for different embodiments. Although someembodiments are discussed with operations performed in a particularorder, these operations may be performed in another logical order.

FIG. 1 is a schematic diagram of a chip 100, in accordance with someembodiments. As shown in FIG. 1, ten metal lines 221-230 are included inthe chip 100, and each of resistors R1-R10 is extracted in each of themetal lines 221-230 respectively. The chip 100 can be a portion or ablock of an IC.

Specifically, the resistors R1-R10 are extracted from data of design forthe IC by Electronic Design Automation (EDA) tools or other circuitsimulation tools. Each of the resistors R1-R10 represents an equivalentresistance of a metal line, and the current passing through the metalline can also be estimated by the above simulation tools. In someembodiments, more than one resistor can be extracted in one metal lineby EDA tool or other circuit simulation tools.

In order to evaluate the failure rate of the chip 100, failure-in-time(FIT) value can be utilized to estimate the failure rate. Specifically,the failure is resulted from the Electro-migration (EM) effect whichmight change the resistance value of resistors R1-R10 in the metal lines210-230. When the resistance value increases above a predeterminedpercentage, it will be determined to be failed.

The FIT value means the failure per one billion device and hour. Inother words, when FIT value is one, it indicates one failure in onethousand products through one million hours, or it may also indicate onefailure in 100 thousand products through 10 thousand hours.

More specifically, the FIT value of a metal line or a verticalinterconnect accesses (VIA) can be calculated by the following equation:

${FIT} = {\frac{\left( {- 10} \right)^{9}}{LT} \times {\ln\left( {1 - {\Phi\left( \frac{\ln\left( {S_{DC}^{n} \times \left( {{LT}\text{/}{MTF}} \right)} \right)}{\sigma} \right)}} \right)}}$

Regarding the above equation, LT is the lifetime of the productexpressed in hours, Φ is a standard normal cumulative distributionfunction. S_(DC) is DC EM severity ratio, which is the ratio between DCcurrent of design and DC EM limit from the foundry design rule. MTF ismedian time to failure in hour, σ is spread in lifetime distribution,and n is current density exponent.

In the embodiment of FIG. 1, each FIT value of resistors R1-R10 in themetal lines 221-230 can be calculated using the equation above. Itshould be noted that resistors R1-R10 are the weak link, which meansthat resistors R1-R10 are independent and not affected by each other.Therefore, the total FIT value of the chip 100 can be calculated bysumming the 10 FIT values of the resistors R1-R10.

FIGS. 2A-2B are schematic diagrams of resistors of a metal line, inaccordance with some embodiments. As shown in FIG. 2A, the metal line201 is connected with two VIAs 301 and 302. Two resistors R11 and R12are extracted by circuit simulation tools, and they are arranged alongthe metal line 201 and between the VIAs 301 and 302. The total FIT valueis the summation of FIT values of resistors R11 and R12.

It should be noted that, regarding the same layout and circuit, theextraction of resistors might be different in accordance with thecircuit simulation tools. As shown in FIG. 2B, the metal line 201 isconnected with two VIAs 301 and 302, which is the same as FIG. 2A.However, three resistors R13, R14 and R15 are extracted by anothercircuit simulation tool which is different from that of FIG. 2A, andthey are arranged along the metal line 201 and between the VIAs 301 and302. The total FIT value is the summation of FIT values of resistorsR13, R14 and R15.

In the embodiments of FIG. 2A and FIG. 2B, although the layout structureand circuit arrangements of metal line 201 and VIAs 301-302 are thesame, the total FIT values are different due to the adopted differentcircuit simulation tools. Even within the same circuit simulation tools,the FIT value will vary corresponding to the criteria of metal linesegment.

FIGS. 3A-3B are schematic diagrams for illustrating nodes and metalsegments of metal line, in accordance with some embodiments. The metalline 202 has two line ends E1 and E2, and it is connected with two VIAs303 and 304 which are upward or downward. In the metal line 202, fiveresistors R16-R20 are extracted by the circuit simulation tools.Resistor R16 is arranged between line end E1 and the VIA 303, resistorsR17-R19 are arranged between the VIAs 303 and 304, and resistor R20 isarranged between the VIA 304 and line end E2.

In some embodiments, the VIA 303 is assigned to be the node N1 by EDAtool or other circuit simulation tools, and the VIA 304 is assigned tobe the node N2. As such, two nodes N1 and N2 are determined based on theVIAs 303 and 304 along the metal line 202. Afterwards, as shown in FIG.3B, three metal segments S1-S3 can be determined according to the nodesN1 and N2 by EDA tool or other circuit simulation tools. The metalsegments S1, S2 and S3 make up the metal line 202. In other words, themetal line 202 is divided into the three metal segments S1, S2 and S3.

As shown in FIG. 3A and FIG. 3B, the metal segment S1 is arrangedbetween the node N1 and line end E1, the metal segment S2 is arrangedbetween the nodes N1 and N2, and the metal segment S3 is arrangedbetween the node N2 and line end E2. Therefore, the metal segment S2 isdefined by two adjacent and different nodes N1 and N2.

Regarding the metal segment S1, FIT value can be evaluated for theresistor R16 in metal line 202. Regarding the metal segment S3, FITvalue can be evaluated for the resistor R20 in metal line 202.

Since three resistors R17-R19 are included by the metal segment S2,three FIT values corresponding to the resistors R17-R19 of the metalsegment S2 can be calculated respectively. In some embodiments, themaximum FIT value is determined to be a representative FIT value of themetal segment S2. In other words, the highest FIT value will be therepresentative FIT value of the metal segment S2.

For example, when the FIT value of the resistor R19 is greater than theother two FIT values of resistors R17 and R18, the FIT value of resistorR19 will be determined to be the representative FIT value for the metalsegment S2.

Regarding the metal segment having more than two resistors, the maximumFIT value is determined to be the representative FIT value of the metalsegment, and other small FIT values will not contribute to therepresentative FIT value. In the embodiments of FIGS. 2A-2B, all FITvalues of the multiple resistors in the metal lines are added to derivethe representative FIT value of a segment of metal line.

Compared to the representative FIT value of embodiments of FIGS. 2A-2B,the representative value of the metal segment S2 of FIG. 3B will becomesmaller. Therefore, the FIT value of the metal segment can be reduced.The process of evaluating the FIT value for the IC becomes efficient andconvenient, regardless of the circuit simulation tools used.

Afterwards, the total FIT value of the IC can be obtained by summing theFIT value and/or the representative FIT value of each of the metalsegments S1-S3. Regarding the metal segment S2, when the FIT value ofthe resistor R19 is greater than the other two FIT values of resistorsR17 and R18, the total FIT value can be obtained by adding the three FITvalues of resistors R16, R19 and R20 of the metal line 202.

The FIT value and/or the representative FIT value of each of the metalsegments are added to derive the total FIT value of the IC. The totalFIT value can be utilized to verify the layout and fabricate the IC.Specifically, when the total FIT value meets the requirement of ICdesign, it means that the layout is certified and the IC can bemanufactured based on the certified layout.

When the total FIT value meets the requirement of IC design, somesemiconductor processes are performed on a wafer to manufacture at leastone IC corresponding to the certified layout. When the total FIT valuedoes not meet the requirement of IC design, it means the layout is notcertified, and the data for designing the IC needs to be revised andmodified.

For example, when the total FIT value is smaller than a threshold value,the EDA tool or circuit simulation tools determine that it meets therequirement of IC design. When the total FIT value is greater than athreshold value, the EDA tool or circuit simulation tools determine thatit does not meet the requirement of IC design.

FIGS. 4A-4B are schematic diagrams for illustrating nodes and metalsegments of a metal line, in accordance with some embodiments. As shownin FIG. 4A, the metal line 203 is connected with VIAs 305 and 306. Theshape of metal line 203 is a cross-junction. Furthermore, the metal line203 includes four branches 203A-203D and an intersection 203E. Branches203A and 203D are perpendicular to the branches 203B and 203C, and eachof the four branches 203A-203D are connected to the intersection 203E.

In some embodiments, as shown in FIG. 4B, the intersection 203E of themetal line 203 is assigned to be the node N3. The VIAs 306 aredetermined to be nodes N4 and N5, and VIAs 305 are determined to benodes N6 and N7. The metal segments S4-S7 can be determined and dividedbased on the nodes N3-N7 by the EDA tool or circuit simulation tools.The metal segment S4 is arranged between nodes N3 and N4, metal segmentS5 is arranged between nodes N3 and N5, metal segment S6 is arrangedbetween nodes N3 and N6, and metal segment S7 is arranged between nodesN3 and N7.

The metal segment S4 includes resistors R41 and R42, metal segment S5includes resistor R43, metal segment S6 includes resistors R45 and R46,metal segment S7 includes resistor R44. The FIT values of each of themetal segments S4-S7 can be calculated accordingly. The representativeFIT values of the metal segments S4-S7 can be determined by the maximumFIT value in each metal segment. Details relating to the calculation ofthe FIT value have been illustrated before, and in the interests ofbrevity they will not be repeated herein.

FIGS. 5A-5B are schematic diagrams for illustrating nodes and metalsegments of a metal line, in accordance with some embodiments. The metalline 204 is connected with VIA array 307 and VIA 308. In the metal line204, four resistors R51-R54 are extracted by EDA tool or circuitsimulation tools.

As shown in FIG. 5A, the VIA array 307 includes a number of VIAs 307Aand 307B. The VIAs 307A and 307B are close to each other to form the VIAarray 307. More specifically, the distance between the VIAs 307A and307B is smaller than line width S204 of the metal line 204. In addition,there is no resistor extracted by the circuit simulation tools betweenthe two VIAs 307A and 307B.

In some embodiments, the VIA array 307 is determined to be node N8, andVIA 308 is node N9. As shown in FIG. 5A and FIG. 5B, metal segment S8 isdetermined between line end E3 and N8, metal segment S9 is determinedbetween nodes N8 and N9, and metal segment S10 is determined betweennode N9 and line end E4. Afterwards, the FIT values of each of the metalsegments S8-S10 can be calculated accordingly. Details of thecalculation of the FIT value have been illustrated before, and will notbe repeated.

FIGS. 6A-6B are schematic diagrams for illustrating nodes and metalsegments of metal lines, in accordance with some embodiments. As shownin FIG. 6A, the metal line 205 can be divided into metal line 205A withline width W205A and metal line 205B with line width W205B. Line widthW205A is greater than line width W205B. VIA 309 is connected to themetal line 205A, and the VIA 310 is connected to the metal line 205B.

As illustrated before, the VIAs 309 and 310 are assigned to be the nodesN10 and N11 respectively. Accordingly, three metal segments S11-S13 canbe determined based on the nodes N10 and N11. Metal Segment S11 includesresistor R61, metal segment S12 includes resistors R62 and R63, andmetal segment S13 includes resistor R64.

It should be noted that a portion of metal line 205A (including resistorR62) and a portion of metal line 205B (including resistor R63) form themetal segment S12. In other words, the metal segment S12 includes anumber of metal lines whose line widths are different. The FIT values ofeach of the metal segments S11-S13 can be calculated accordingly. Therepresentative FIT values of the metal segments 11-S13 can be determinedby the maximum FIT value in each metal segment. Details relating to thecalculation of the FIT value have been illustrated before, and in theinterests of brevity they will not be repeated herein.

FIG. 7 is a schematic diagram illustrating current direction with nodesand metal segments of a metal line, in accordance with some embodiments.The current direction is considered for evaluating the FIT value. ThreeVIAs 311-313 are connected to the metal line 206. The VIA 311 isdetermined to be node N12, VIA 313 is determined to be node N13.Resistors R71-R74 are arranged between nodes N12 and N13.

In some embodiments, as shown in FIG. 7, whether or not a current passesthrough the VIA is detected. When the current passes through the VIAs,the VIA is determined to be the node. In other words, when no currentpasses through the VIA, the VIA will not be regarded as a node.

As shown in FIG. 7, the current I1 passes through the VIA 311, the metalline 206 and the VIA 313. Since the current does not pass through theVIA 312, the VIA 312 will not be determined to be a node. Therefore,there are two nodes N12 and N13 along the metal line 206, and the metalsegment S11 can be determined based on the nodes N12 and N13 in order toevaluate the FIT value.

FIG. 8 is a schematic diagram illustrating current direction withbranches of a metal line, in accordance with some embodiments. Thecurrent direction is considered for evaluate the FIT value. The metalline 207 is connected with VIAs 314 and 315. The shape of metal line 207is a cross-junction. Furthermore, the metal line 207 includes fourbranches 207A-207D and an intersection 207E. Branches 207A and 207D areperpendicular to the branches 207B and 207C, and each of the fourbranches 207A-207D are connected to the intersection 207E.

In some embodiments, as shown in FIG. 8, whether or not a current passesthrough more than two branches of the intersection is detected. When thecurrent passes through more than two branches of the intersection, theintersection is determined to be the node. In other words, when thecurrent does not pass through more than two branches of theintersection, the intersection will not be regarded as a node.

As shown in FIG. 8, the current I2 passes through the VIA 314, thebranches 207A-207B, and the VIA 314. In other words, the current passesthrough two branches 207A-207B, it does not pass through more than twobranches. Since the current does not pass through the branches 207C and207D, the intersection 207E will not be determined to be a node.

Therefore, current passes through nodes N14 and N 15, and the metalsegment S12 can be determined based on the nodes N14 and N15 in order toevaluate the FIT value. It should be noted that, because the currentdoes not pass through the branches 207C and 207D, the branches 207C and207D will not be regarded as metal segments to estimate FIT values.

FIGS. 9A-9B are schematic diagrams for illustrating VIAs and metallines, in accordance with some embodiments. Four VIAs 316A-316D areconnected to the metal lines 208 and 209, and the four VIAs 316A-316Dmake up the VIA array 316. In some embodiments, as shown in FIG. 9A, FITvalues for each of the VIAs 316A-316D are calculated. Afterwards, themaximum of the calculated FIT values is determined to be therepresentative FIT value of the VIA array 316. Since FIT value of eachof VIAs 316A-316D is calculated, the representative FIT value of the VIAarray 316 will be accurate.

As shown in FIG. 9B, in some embodiments, total current of the VIA array316 and total electro-migration (EM) limit of the VIA array 316 arecalculated to evaluate FIT value of the VIA array 316. Because totalcurrent and total EM limit are utilized to estimate FIT value withoutconsidering each VIA 316A-316D individually, the FIT value can beevaluated quickly.

FIG. 10 is a flow chart of a method illustrating the operations forevaluating FIT value, in accordance with some embodiments. In operation1002, data of design (i.e., layout) of an IC is accessed from, forexample, cell information, foundry data, design rules and technologyfile. Afterwards, operations 1004 and 1008 will be executed in themethod.

In operation 1004, resistors and capacitors (RC) are extracted from theaccessed data, and RC netlist can be developed accordingly. The RCnetlist is a schematic illustrating the arrangement of resistors andcapacitors in metal lines of the data of an IC. Afterwards, in operation1006, currents passing through each resistor are simulated by circuitsimulation tools.

Furthermore, in operation 1008, layout dimension is obtained based onthe data of design of IC. In operation 1010, the EM limit of eachresistor can be estimated. Afterwards, in operation 1012, which isexecuted after operations 1006 and 1010, the DC EM severity ratio can becalculated according to the equation as shown before.

In operation 1014, the FIT value for each resistor is evaluated. Detailsof the method for evaluating the FIT value will be illustrated in theflow charts of FIG. 11-12. In operation 1016, each of the FIT values isadded. In operation 1018, the total FIT value for the IC can be derivedaccordingly.

FIG. 11 is a flow chart of a method illustrating the operations forevaluating FIT value, in accordance with some embodiments. In operation1102, a number of nodes on metal lines and/or VIAs are picked.Specifically, in some embodiments, vias or an intersection of metallines can be picked to be the nodes by the EDA tool or circuitsimulation tools. In operation 1104, a number of metal segments aredetermined based on the nodes.

Afterwards, in operation 1106, current directions along each of themetal lines and/or VIAs are determined. In operation 1108, the FIT valueof each of the metal segments is evaluated. The evaluation of FIT valuehas been illustrated before, and will not be repeated again.

In operation 1110, a total FIT value for the IC can be derived bysumming each FIT value. More specifically, the total FIT value for theIC can be derived by summing each of the FIT values of the metalsegments, or summing each of the FIT values or each of therepresentative FIT values of the metal segments. It should be noted thatoperation 1106 is optional and can be neglected in performing themethod.

FIG. 12 is a flow chart of a method illustrating the operations forevaluating FIT value, in accordance with some embodiments. In operation1202, whether a VIA is a single VIA or a VIA array is determined. If itis a single VIA, operation 1204 will be executed. If it is a VIA array,either operation 1206 or 1210 is determined.

In operation 1204, the FIT value of the signal VIA is calculated.Furthermore, in operation 1206, the total current and total EM limit ofthe VIA array are calculated. In operation 1208, the FIT value of theVIA array is evaluated.

In operation 1210, a FIT value for each VIA is calculated. In operation1212, the maximum FIT value is selected to be the representative FITvalue of the VIA array. In operation 1214, each of the FIT values isadded.

FIG. 13 is a block diagram of a computer system for evaluating FITvalue, in accordance with some embodiments. One or more of the toolsand/or systems and/or operations described with respect to FIGS. 1-12 isrealized in some embodiments by one or more computer systems 1300 ofFIG. 13. The computer system 1300 includes a processor 1310, a memory1320, a network interface (I/F) 1330, a display 1340, an input/output(I/O) device 1350, and one or more hardware components 1360communicatively coupled via a bus 1370 or another interconnectioncommunication mechanism.

The memory 1320 comprises, in some embodiments, a random access memory(RAM) and/or other dynamic storage device and/or read only memory (ROM)and/or other static storage devices, coupled to the bus 1370 for storingdata and/or instructions to be executed by the processor 1310. Thememory 1320 is also used, in some embodiments, for storing temporaryvariables or other intermediate information during execution ofinstructions to be executed by the processor 1310.

The display 1340 is utilized to display the RC netlist and the layout ofthe IC. The display 1340 can be liquid-crystal panels or touch displaypanels. The I/O device 1350 includes an input device, an output deviceand/or a combined input/output device for enabling user interaction withthe computer system 1300. An input device comprises, for example, akeyboard, keypad, mouse, trackball, trackpad, and/or cursor directionkeys for communicating information and commands to the processor 1310.An output device comprises, for example, a display, a printer, a voicesynthesizer, etc. for communicating information to the user.

In some embodiments, one or more operations and/or functions of thetools and/or systems described with respect to FIGS. 1-13 are realizedby the processor 1310, which is programmed for performing suchoperations and/or functions. One or more of the memory 1320, the I/F1330, the display 1340, the I/O device 1350, the hardware components1360, and the bus 1370 is/are operable to receive instructions, data,design rules, netlists, layouts, models and/or other parameters forprocessing by the processor 1310.

In some embodiments, one or more of the operations and/or functions ofthe tools and/or systems described with respect to FIGS. 1-13 is/areimplemented by specially configured hardware (e.g., by one or moreapplication-specific integrated circuits or ASIC(s)) which is/areincluded) separate from or in lieu of the processor 1310. Someembodiments incorporate more than one of the described operations and/orfunctions in a single ASIC.

In some embodiments, the operations and/or functions are realized asfunctions of a program stored in a non-transitory computer readablerecording medium. Examples of a non-transitory computer readablerecording medium include, but are not limited to, external/removableand/or internal/built-in storage or memory unit, e.g., one or more of anoptical disk, such as a DVD, a magnetic disk, such as a hard disk, asemiconductor memory, such as a ROM, a RAM, a memory card, and the like.

By assigning nodes and determining metal segments along the metal lines,the FIT values can be evaluated based on the nodes and metal segments.The evaluation of the FIT value is independent with the adopted circuitsimulation tools. Therefore, the process for evaluating FIT value issimplified and efficient.

In accordance with some embodiments, a FIT evaluation method for an ICis provided. The FIT evaluation method includes accessing datarepresenting a layout of the IC comprising a number of metal lines and anumber of VIAs; picking a plurality of nodes along the metal lines; anddetermining FIT value for each of the VIAs to verify the layout andfabricate the IC.

In accordance with some embodiments, a FIT evaluation method for an ICis provided. The FIT evaluation method includes determining a pluralityof nodes along a plurality of metal lines and a plurality of verticalinterconnect accesses (VIAs) from data representing a layout of the IC;and evaluating FIT value for each of the VIAs, wherein FIT values forthe VIAs are utilized to verify the layout and fabricate the IC.

In accordance with some embodiments, the disclosure provides anon-transitory computer-readable medium containing instructions which,when executed by a processor of a computer system, cause the processorto execute a FIT evaluation method including determining a plurality ofnodes along a plurality of metal lines and a plurality of verticalinterconnect accesses (VIAs) from data representing a layout of anintegrated circuit (IC); and evaluating FIT value for each of the VIAs,wherein FIT values of the VIAs are utilized to verify the layout andfabricate the IC.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A failure-in-time (FIT) evaluation method for anintegrated circuit (IC), comprising: accessing data representing alayout of the IC comprising a plurality of metal lines and a pluralityof vertical interconnect accesses (VIAs); picking a plurality of nodesalong the metal lines; and determining FIT value for each of the VIAs toverify the layout and fabricate the IC.
 2. The FIT evaluation method asclaimed in claim 1, wherein picking the plurality of nodes along themetal lines further comprises assigning the VIAs to be the nodes.
 3. TheFIT evaluation method as claimed in claim 2, wherein assigning the VIAsto be the nodes further comprises detecting whether or not a currentpasses through one of the VIAs, and assigning the one of the VIAs to beone of the nodes when the current passes through the one of the VIAs. 4.The FIT evaluation method as claimed in claim 1, wherein picking aplurality of nodes along the metal lines further comprises assigning oneof the VIAs or an intersection of the metal lines to be one of thenodes.
 5. The FIT evaluation method as claimed in claim 4, whereinassigning intersections of the metal lines to be the nodes furthercomprises detecting whether or not a current passes through more thantwo branches of the intersection, and assigning the intersection to bethe one of the nodes when the current passes through more than twobranches.
 6. The FIT evaluation method as claimed in claim 1, whereinthe data representing the layout of the IC comprises a plurality ofresistors.
 7. The FIT evaluation method as claimed in claim 6, furthercomprising evaluating an electro-migration (EM) limit of each of theresistors.
 8. The FIT evaluation method as claimed in claim 7, furthercomprising calculating a DC EM severity ratio of each of the resistors.9. The FIT evaluation method as claimed in claim 1, wherein the VIAsform a VIA array, and picking the nodes along the metal lines furthercomprises assigning the VIA array to be one of the nodes.
 10. The FITevaluation method as claimed in claim 9, wherein determining a FIT valuefor each of the VIAs comprises calculating total current and total EMlimits to evaluate FIT value of the VIA array.
 11. The FIT evaluationmethod as claimed in claim 9, wherein determining the FIT value for eachof the VIAs comprises determining a maximum for the calculated FITvalues to be a representative FIT value of the VIA array.
 12. Afailure-in-time (FIT) evaluation method for an integrated circuit (IC),comprising: determining a plurality of nodes along a plurality of metallines and a plurality of vertical interconnect accesses (VIAs) from datarepresenting a layout of the IC; and evaluating FIT value for each ofthe VIAs, wherein FIT values for the VIAs are utilized to verify thelayout and fabricate the IC.
 13. The FIT evaluation method as claimed inclaim 12, wherein determining the nodes on the plurality of metal linesand VIAs comprises: assigning the VIAs to be the nodes or assigningintersections of the metal lines to be the nodes.
 14. The FIT evaluationmethod as claimed in claim 12, wherein the data representing a layout ofthe IC comprises a plurality of resistor.
 15. The FIT evaluation methodas claimed in claim 14, further comprising evaluating anelectro-migration (EM) limit of each of the resistors.
 16. The FITevaluation method as claimed in claim 15, further comprising calculatinga DC EM severity ratio of each of the resistors.
 17. A non-transitorycomputer-readable medium containing instructions which, when executed bya processor of a computer system, cause the processor to execute a FITevaluation method comprising: determining a plurality of nodes along aplurality of metal lines and a plurality of vertical interconnectaccesses (VIAs) from data representing a layout of an integrated circuit(IC); and evaluating FIT value for each of the VIAs, wherein FIT valuesof the VIAs are utilized to verify the layout and fabricate the IC. 18.The non-transitory computer-readable medium as claimed in claim 17,wherein determining the nodes on the plurality of metal lines and theplurality of VIAs comprises assigning the VIAs to be the nodes.
 19. Thenon-transitory computer-readable medium as claimed in claim 18, whereinthe VIAs form a VIA array, and picking the nodes along the metal linesfurther comprises assigning the VIA array to be one of the nodes. 20.The non-transitory computer-readable medium as claimed in claim 18,wherein evaluating the FIT value for each of the VIAs comprisesdetermining a maximum for the calculated FIT values to be arepresentative FIT value of the VIA array.